When displaying television programs, or data from optical disk, such as CD (Compact Disk), DVD (Digital Versatile Disk), BD (Blu-Ray Disk), or any other data media carriers, a video may have various elements overlaid over it (referred to as “overlay data” in the following). A typical example is subtitles usually placed at the bottom or top of video area. Other overlay may also include scoreboards, news tickers, or logos.
FIG. 1 illustrates a conventional display where video data placed in a video plane and overlay data placed in an overlay plane are displayed. Here, the overlay data (e.g. subtitles) is located at the bottom of the video. As a consequence, part of video area is occulted by the overlay data.
To solve this problem, some techniques are known for detecting semantic features and adaptively adjusting the placement of the overlay data in the display area.
A method of adaptive the placement of overlay data in video is disclosed in US 2002/0196370 A1. This document describes a method of placing overlay elements in images of a digital video so that desirable viewing areas of the images are not occluded by the overlay element. This method includes extracting frames from the video, each of the frames defining an image which may have one or more desirable viewing areas. For each frame an area is selected in the image for placing an overlay element and the percentage the overlay element overlaps the desirable viewing areas is determined for the selected area. The overlay element is placed in the selected area if the percentage is below a maximum allowed predetermined percentage of overlapping. If it is not, one or more other areas in the image are selected and/or the size, shape, aspect ratio of the overlay element is changed until a position and/or size, shape, aspect ratio is found which minimizes occlusion of the desirable viewing areas in the image.
This known method has however some limitations.
First, this method determines in real-time a percentage of the overlay data which overlap each desirable viewing area in each video frame so as to find the most suitable area to place the overlay data. This method is thus complex and requires a lot of expensive data processing means.
Secondly, even if overlay data are placed in the best desirable area of video, they still overlap the video, to the detriment of overall visual comfort for the viewer.